Chemicals:
| 2 mmol m-nitroaniline / 96 % ethanol (276 mg / 20 mL
| | 4 mmol 2-naphthol / 96 % ethanol (577 mg / 20 mL)
| | 0.2 mmol 1-naphthylamine / 96 % ethanol (29 mg / 20 mL)
| | 0.5 % aqueous NaNO2 solution
| | conc. HCl
| | 2 N NaOH | |
Hazards and safety precautions:
 |
Aniline is highly toxic. Possible carcinogen. Possible mutagen. Possible sensitizer. Cyanotic reagent. Readily absorbed
through the skin.
1-Naphthylamine: at high concentrations poisining symptoms similar to aniline toxication.
m-Nitroaniline is toxic by ingestion, inhalation or through skin contact |
  |
NaNO2 is toxic if swallowed. Severe eye irritant. Respiratory and skin irritant. May act as a carcinogen for
chronic exposure. |
 |
2-Naphthol is harmful if swallowed or inhaled. May be harmful in contact with the skin. Eye, skin and respiratory irritant.
|
 |
Conc. hydrochloric acid is extremely corrosive. Inhalation of vapour can cause serious injury. Ingestion may be fatal.
Liquid can cause severe damage to skin and eyes. |
Safety goggles and protective gloves required - well ventilated room. The preparation of the ethanolic solutions of
1-naphthylamine, m-nitroaniline and 2-naphthol should be performed under a laboratory fume hood!
Experimental procedure:
1 mL ethanolic 2-naphthol solution is pipetted into each of the two test tubes (T1, T2). The tubes T3 and T4 contain the ethanolic
solutions of
m-nitroaniline and 1-naphthylamine respectively. The solutions in T1 and T2 are mixed with conc. HCl. Afterwards, some drops of
NaNO2 solution are added to the solutions in T3 and T4.
| Test tube 1
| 1 mL of ethanolic 2-naphthol solution 1 drop of conc. HCl
| Test tube 2
| 1 mL of ethanolic 2-naphthol solution 1 drop of conc. HCl
| Test tube 3
| 1 mL of ethanolic m-nitroaniline solution 5 drops of NaNO2 solution
| Test tube 4
| 1 mL of ethanolic 1-naphthylamine solution 5 drops of NaNO2 solution
| | | |
5 drops of the solutions of T3 or T4 are given to the solutions in T1 or T2. Afterwards 5 drops NaOH are added to the dye
solutions formed.
Results:
Photo 1 |
Photo 2 |
|
|
| Color
| after addition of NaOH
| | Test tube 1
| yellow
| yellow-orange
| | Test tube 2
| violet
| orange-red |
|
Discussion:
· Typical para azo dyes "Nitroaniline Orange" Photo 1 and "Ice
Bordeaux" Photo 2 are formed by coupling of 2-naphthol with diazotised m-nitroaniline and 1-naphthylamine
respectively (1, 2).
· In practice the fiber is impregnated with 2-naphthol and a wetting agent. Afterwards the dye is
developed by immersing the dry textile in a ice-cooled bath containing diazotised amine.
Reference:
 Demonstration Experiment on Video
Azo Coupling
General experimental instructions and index of experiments
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